The present invention concerns a container for the storage and transport of nuclear fuel, in particular irradiated nuclear fuel after it has been removed from a nuclear reactor and before the fuel is reprocessed to separate reusable nuclear fuel materials from the products of nuclear fission. Such a container generally accommodates a plurality of nuclear fuel element assemblies and for convenience is termed a multi-element bottle (MEB).
A MEB comprises an elongate cylindrical bottle closed at one end and having a removable lid at its opposite end, the lid being fitted with a seal which seats on a flange at the end of the bottle and being releasably secured to the flange by bolts. The bottle can accommodate a plurality of fuel element assemblies which can be located in compartments which allow for free circulation of cooling water whilst retaining the fuel in a criticality safe array. Typically the bottle can contain seven individual compartments but the number and arrangement of the compartments within the bottle is a matter of design choice. The bottle is contained within a flask for transport and both the bottle and the flask are filled with water. Ullage space within the bottle and the flask allow for thermal expansion of the water under normal conditions.
In the event of an accident involving fire and resulting in a rapid rise in temperature with consequent rise in pressure it is required to provide additional ullage in order to reduce the pressure within the bottle and the flask. The invention provides a bottle having additional ullage for accident conditions.